Television receiver chassis construction



Oct. 2, 1951 F. L. WEDIG 2,570,017

TELEVISION RECEIVER cHAssIs CONSTRUCTION Filed Nov. 2, 1949 2Sheets-Sheet 1 IN V EN TOR. FRANK L. WED/G Oct. 2, 1951 F. L. WEDIG2,570,017

TELEVISION RECEIVER CHASSIS CONSTRUCTION Filed Nov. 2, 1949 2 Sheets-Sheet 2 SIGNAL INPUT IN VEN TOR. FRANK L. WED/6 Patented Oct. 2, 1951TELE ON RECEIVE HASSIS. CONSTRUCTION Frank L. Wedig; Cincinnati, Ohio,assignor to Avco. Manufacturing; Corporation, Cincinnati, Ohio, a.corporation of Delaware;

Application November 2, 19/49, Serial No, 125,071

The present invention relates to an improved chassis construction fordirect-power-line-connected (power-transformerless) type televisionreceivers. The primary object of the present invention is to providesuch a chassis construction that a common metallic element forsupporting the various receiver components may be maintained at asubstantial potential difference with respect to true ground withoutpresenting a shock hazard to the user or operator and without requiringthe individual insulation of manually operative control shafts andspecial precautions forindividually insulating the main chassismountings from the cabinet.

Alternately stated, the primary object of the invention is to provide asimple construction for insulating the manually operative controls from"a hot common metallic support for the various receiver components, thissupport being directly connected to one side of the power line.

Another basic object of the invention is to provide a chassisconstruction whichcan be directly mounted in a wooden cabinet withoutthe taking of special precautions to insulate the bottom of the metallicchassis from the wood.

Still another object of the invention is to provide a chassisconstruction in which the main chassis body is cold, i. e., at trueground potential so that it can function as part of the exterior of thereceiver, in conjunction with a subchassis so arranged that theconstruction provides the lowest possible impedance in RF returns, suchas those between the various tuned circuits and ground. In the interestsof receiver efliciency and stability it is desirable that there beprovided a low impedance path between the vacuum tube circuits and thecommon base plate, at least for radio frequencies. An object of this"invention is to make that impedance as low as possible, because highcommon impedances in these circuits result in undesired stray couplings.

In the usual receiver installations one side of J the supply line isconnected to ground and it is impossible to connect one side of theconventional chassis construction to ground, when an unpalarizedpowerplug is employed, because of the existence of the hazard of adirect short circuit across the supply line. This means that the usualone-piece metallic chassis construction may be hot and at a highpotential difference with respect to true ground when the tube cathodesand power supply lines are directly connected to the chassis, forexample. In or- 1 derto prevent this potential difference from con 2Claimsi L. 250-16,).

2 V stituting a shock hazard to the user of the. receiver, it isnecessary to insulate the, mannually operative parts or shafts of thevarious controls from the conventional hot chassis, also to insulate themetallic supporting mountings at the bottom of the chassis constructionfrom the wooden cabinet, since underwriters" requiree ments do notpermit a hot chassis to be mount..- ed directly on wood, the latterbeing regarded as a poor insulator.

When it is considered that a television receiver generally includes alarge number of controls such as the contrast control, the brilliancycontrol, the volume control, the horizontal frequency control, thehorizontal lock control, and so forth, it becomes apparent that theindividual isolation of the manually operative shafts of the variouscontrols from a hot chassis presents a very costly engineering andconstruction job. The cost and difliculties involved are considerablyaggravated when it is borne in mind that the lower mountings which areemployed to support the conventional chassis must also be individuallyspecially insulated from a wood cabinet, since no hot metallic elementsare permitted directly to contact such a receiver cabinet.

The chassis construction provided in accordance with the, inventionconsists briefly of a common metallic plate which is connected to oneside of the power line to provide an electrical ground or chassis groundfor the various receiver components. To this plate are connected all ofthe circuit elements requiring a common or chassis ground. This plate ismounted atop a box-like main chassis or tray and the plate is insulatedfrom the main chassis member or tray by a plurality of insulatingsupports. The common plate may be "hotwhile the main chassis tray iscold. The chassis tray therefore presents no shock hazard to the userand the users controls which project forwardly from and through the traydo not have to be insulated therefrom. The very simple and inexpensiveinsulating means between the top plate and tray is provided in lieu ofthe large number of complex individual insulating expedients heretoforeemployed with respect to each control and each mounting between chassisand cabinet. For a better understanding of the present invention,together with other and iurther o jects, advanta s, and p i it es th rerefe en is mad to the accom any n drawings. in which there, is shown anil ustrative pre er-re form of chassis construction in accordance withthe invention.

In the drawings:

Fig. 1 is a front perspective view of a television receiver having achassis construction in accordance with the invention;

Fig. 2 is a fragmentary elevational sectional view taken along the line22, looking in the direction of the arrows; and

Fig. 3 is a circuit schematic showing the connections of the powersupply and other illustrative receiver components employed with achassis construction in accordance with the invention.

Referring now specifically to Fig. 3 of the drawings, the novel chassisconstruction in accordance with the invention comprises a metallicchassis tray II, the front wall 12 Of which is shown in section, and ametallic top plate or lid l3, shown in section, suitably insulated fromthe tray. The tray is flanged inwardly at the top, as indicated at Hill.

The supply mains l4, [5, one of which is connected to true ground at l6,terminate at socket l8, which receives the contact prongs of aconventional plug H3, at the end of supply conductors 20, 2|. Conductor2| is directly connected to the metallic top plate l3. Conductor 28 isin series with a resistor 22 and rectifier 23. The power supply iscompleted by a series choke 24 and a pair of shunt filter capacitors 25,26. The power supply output terminals are shown at 28 (+13) and 2! (B),the latter being shown at the point of connection of supply lineconductor 2| and top plate [3. It will be understood that the whole ofplate I3 constitutes a chassis ground for the various circuitcomponents. This plate, as indicated, is directly connected to one side(2|) of the power line.

As shown in Fig. 1, the various television receiver components aremounted on plate l3. In the specific illustrative example shown, thesecomponents may comprise:

Cathode ray tube 30 Loud speaker 3| Deflection yoke 32 Focus coil 33Horizontal output transformer 34 Synchronizing signal separator tube 35Synchronizing signal amplifier tube 36 Video detector tube 31 Videoamplifier tube 38 First, second, third, and fourth intermediatefrequency amplifier tubes 39, 48, 4|, and 42 Horizontal damper tube 43Horizontal oscillator and control tube 44 Blocking oscillatortransformer 45 Audio power output tube 46 Electrolytic capacitor 48Audio amplifier tube 49 Radio detector windings 50 Vertical oscillatorand output tube Radio detector tube 52 Horizontal driver tube 53 The R.F. amplifier tube 54, mixer tube 55, and oscillator tube 56 aresupported on a metallic bracket 51, secured within an opening 58 onplate l3.

The specific arrangement of the components supported by plate l3, asherein described, is exemplary and the invention is not limited to theparticular arrangement illustrated in Fig. 1.

Referring again to Fig. 3, there is shown a portion of the signalchannel of a typical intercarrier-sound type of receiver utilizing theinvention.

This channel comprises a fourth I. F. amplifier stage including a tube42. The signal input circuit of this tube is tuned by a circuitcomprising an adjustable iron core inductance 6|, tuned by its owndistributed capacitance and shunted by a damping resistor 63, this tunedgrid circuit being returned to top plate 13, which provides a commonground. The anode of tube 42 is connected to a plate load inductance 64.The junction of the screen grid and plate load is connected to highpotential terminal 28 of the power supply. The cathode is connected totop plate [3, through a bias resistor H, by-passed by capacitor 12.

The output circuit of tube 42 is coupledtoavideo detector tube 31 by acapacitor 55. The detector circuit network includes peaking inductors85, 81, capacitors '68, 68, and resistor 10, this detector network beingessentially the same as that disclosed in the copending patentapplication of Francis A. Wissel and Norman W. Parker, entitledAutomatic Gain Control, Serial No. 102,176, filed in the U. S. PatentOffice on June 30, 1949, and assigned to the same assignee as thepresent application and invention.

The detector output circuit is coupled by a series peaking inductor 13to the input circuit of a video amplifier tube 38. Contrast is varied byshort-circuiting various portions of cathode resistor 14 by anadjustable contact 15, connected to top plate [3. The cathode of tube 38is returned to the common ground provided by top plate l3. The anode oftube 38 is connected to a parallel combination of peaking coil 16 anddamping resistor 11, which in turn is connected to a resonant circuitcomprising inductance 18 and capacitor 19. The anode of tube 38 isconnected to the high-potential terminal 28 of the power supply throughthe D. C. path provided by inductors l6 and I8, shunt peaking inductor88 and load resistor 8i. The sound signals are taken off by a circuit(not shown) inductively coupled to winding 18. The showing of tubes 42,31, and 38 is made for the purpose of showing typical methods by whichcathodes and tuned circuits may be returned to the common groundprovided by top plate l3, thereby minimizing undesired couplingsbetween, and stray disturbances aifecting, the various tube circuits. Itis to be particularly noted that the invention accomplishes thisadvantage without presenting a shock hazard to the operator.

Resistor l4 and sliding contact 15 are symbolically shown in Fig. 3, indotted outline, within the body of a standard control unit or rheostat82. This unit has the usual metallic manual control shaft 83, whichrotates within a journal 84 provided by a metallic boss projecting fromthe body of the rheostat. The rheostat is of any suitable conventionalconstruction such that the resistor 14 and contact 15, or equivalents,are insulated from the exterior of body 85 and brought out to terminallugs 86, 81, and 88.

The boss 84 and shaft 83 project through an opening in the front wall 12of chassis tray ll, so that the contrast control 14, I5 is located inits customary position, readily available to the operator, in fact inthe position which has become standard in television receivers. This isaccomplished without taking any special precautions whatever forinsulating shaft 83 and boss 84 from the metallic flange I2. Heretofore,in the manufacture of television receivers, it has been necessary totake particular precautions to insulate such bosses and shafts orequivalents from the front flange of the chassis, in order to preventthe existence of a shock hazard to the user. This shock hazard existedwhenever the front flange is hot or may become hot. The construction inaccordance with the present invention insures that this front flangewill be cold at all. times.

In accordance with the invention the top plate I3 is mounted on andinsulated from the chassis tray I I by a plurality of mountings such asthose illustrated at 90, 9|, 92, and 93 in Fig. 1. Mounting 9| isillustrated in detail in Fig. 2. The main chassis tray II is flangedinwardly at the top as indicated at I and is suitably apertured andthreaded to receive the shank IllI of a bolt I02. The head of this boltreposes on the top flange I 03 of a metallic bushing I04. Bolt I02 andbushing I 04 are maintained in cold condition by an insulating washerI05 which is formed with an annular groove I06. Top plate I3 is suitablyapertured to define an annular shoulder I 01 which is received withingroove I06. Washer IDS is made of rubber or suitable flexible insulationwhich may be deformed and manually pressed into place. Washer I05performs the function of electrically isolating top plate I3 fromchassis tra I I. It will be understood that the mountings 90, 9|, 92,and 93 are of substantially similar construction and that other suitablemountings which isolate top plate I3 from chassis tray I I may beemployed within the spirit and scope of the appended claims. Thus itwill be seen that the invention provides such a chassis constructionthat the common metallic element I3 for supporting the various receivercomponents (such as those illustrated in Fig. 1) may be maintained hotor at a substantial potential difference with respect to true ground (1.e., the potential level of the operator) without presenting a shockhazard to the operator and without requiring the individual insulationof manually operative control shafts such as shaft 83 in Fig. 2.Additionally, this chassis construction requires no special precautionsfor insulating the bottom of the tray I I from a wooden cabinet, forexample. Further, the tray I I can function as a part of the exterior ofthe receiver, minimizing the expense of cabinetry. When it is consideredthat television receivers comprise a, large number of controls (of whichthe contrast control herein shown is simply representative), such as thecontrast control, the brilliancy control, the volume control, thehorizontal frequency control, the horizontal lock control, and so forth,it will be understood that very significant economies in engineering andmanufacturing may be accomplished through the practice of the presentinvention.

While there has been shown and described what is considered to be thepreferred embodiment of the present invention, it will be obvious tothose skilled in the art that various modifications and substitutions ofequivalents may be made therein without departing from the true scope ofthe invention as defined by the appended claims.

I claim: I

1. A chassis construction for a television receiver, of the type whichincludes radio frequency selector, frequency-changing, and amplifiercircuits, which receiver is energized from two-conductor mains, one ofwhich may be at the potential level of the operator, and which receiverincludes contrast and other control units having metallic controlshafts, comprising: a metallic box-like tray, formed with an open topand individual apertures, for providing a mechanical support for themanually operated shafts and outwardly projecting metal parts of saidcontrol units, said shafts projecting through said apertures, a metallictop plate which substantially closes said tray and provides a supportfor said circuits, means for mounting said circuits, and meanscomprising a plurality of insulating spacers securing said top plate toand electrically insulating it from said tray for the purpose ofpreventing the connection of one of said mains or an equivalentpotential point to said top plate from creating a potential differencebetween said tray and the operator, whereby said shafts and said metalparts do not present any shock hazard to the operator and may directlycontact sa1d tray, and means for connecting one of said mains to saidtop plate.

2. A chassis construction Ior a television receiver of the type which isenergized from twoconductor mains and which includes control unitshaving projecting manually operated metal shafts, comprising a metallicbox-like tray, formed with an open top and individual apertures forproviding a mechanical support for said shafts, said shafts projectingthrough said apertures, a metallic lid panel which substantially closessaid tray, means comprising a plurality of insulating spacers securingsaid lid panel to and electrically isolating it from said tray for thepurpose of preventing the connection of one of said mains or anequivalent potential point to said lid from creating a potentialdifference between said tray and the operator, whereby said tray doesnot present any shock hazard to the operator, and means for connectingsaid one of said mains to said lid panel.

FRANK L. WEDIG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,087,073 Smith July 13, 19372,443,449 Fry June 15, 1948 2,458,365 Fyler Jan. 4, 1949 FOREIGN PATENTSNumber Country Date 414,819 Great Britain Aug. 15 1934 457,723 GreatBritain Dec. 4, 1936

